Bug Description

[SRU Justification]
The assoc_array_insert_into_terminal_node function in lib/assoc_array.c in
the Linux kernel before 4.13.11 mishandles node splitting, which allows
local users to cause a denial of service (NULL pointer dereference and
panic) via a crafted application, as demonstrated by the keyring key type,
and key addition and link creation operations.

The "add_key04" from the LTP syscall tests will cause kernel oops on a testing node with Trusty kernel installed. And it will make incoming ssh connection hang (bug 1775158)

[Test Case]
This issue can easily be reproduced with the "add_key04" test from the LTP syscall test suite.

[Regression-potential]
Low risk for causing regression.
No additional function was added, only an identifier got removed.
This fix has already landed in Xenial / Artful, and it's still in the mainline tree since then.

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-trusty' to 'verification-done-trusty'. If the problem still exists, change the tag 'verification-needed-trusty' to 'verification-failed-trusty'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.